Looking at Cracks
© Frank Ford, 7/2/98; Photos by FF, 61/98-7/1/98
Fine stringed instruments are usually made of solid, but thin woods. In fact, the wood is so thin that it can break rather easily when hit, or when it is subjected to extremes of humidity and temperature. To confuse the issue, the finish can crack with temperature and humidity changes, too. Sometimes it's difficult to tell the difference between a structural crack in the wood and a crack in just the finish.
Musicians are aware that cracks are never a good thing, and that most of the time they should be repaired and/or reinforced. But the first question is, "Do you think it goes all the way through?" The presumption is that if the crack is only in the finish, then it never needs to be repaired to maintain structural integrity.
I've taken some pictures of instrument cracks to illustrate some of the "classic" structural cracks, to give you some idea of what I look for when I examine an instrument.
Let's start with the most obvious kind:
No question what happened here. The side got hit, and hard! In fact, the side is punctured. There is finish damage indicating that it was a hard object, and the wood fibers are smashed inward.
Here's an obvious crack in a spruce top:
You can tell that it goes all the way through the wood because the crack appears "open" and the wood is "puckered" upward.
This crack is open in the opposite direction. You can be sure that it goes all the way through because even though it's perfectly tight, it "folds" inward:
Whenever you see this kind of crack on the outside, you can bet it looks like this inside, where the crack bends wide open:
This Martin 0-16 has a crack near the fingerboard:
There is a series of finish cracks that have no structural significance, and there is also a tight, flat crack in the spruce. It's easy to see which crack is the structural one because the finish is shattered along its edges where the lacquer was broken, probably as the two edges moved up and down against each other. Not all lacquer checks with shattered edges are structural cracks, but when it's the only one of dozens that has shattered edges, chances are it's a structural crack in a field of finish cracks.
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